1. Field of the Invention
The present invention relates to a method of controlling feed in a centerless veneer lathe and also to an apparatus for the same.
2. Description of the Related Art
In a known technique of peeling veneers from a log under a centerless or spindleless condition, spindles are moved away from the log at a convenient time in the process of veneer peeling operation or alternatively spindles are not used at all from the beginning of the veneer peeling operation. In such a veneer lathe under the centerless condition (hereinafter may be referred to as centerless veneer lathe), the torque required for the peeling operation is only given from a peripheral drive system. The feed control process applied to such centerless veneer lathes controls the feed rate of a feed mechanism in accordance with the theoretical rotating speed of the log driven by the peripheral drive system. When a slippage of the peripheral drive system or a variation in incising depth of the peripheral drive system into the log causes a significant difference between the actual rotating speed and the theoretical rotating speed, however, the conventional feed control process can not accurately control the feed rate, thereby resulting in errors in thickness of veneers peeled from the log.
In the U.S. Pat. No. 5,141,038 (JAPANESE PATENT LAYING-OPEN GAZETTE No. 4-65201) under the title of `Apparatus for feed controlling in a centerless veneer lathe`, the inventor has proposed an improved structure of centerless veneer lathe, which includes a speed measuring device engaged with the peripheral surface of a log for measuring the rotating speed of the log. This improved structure controls the feed rate of the feed mechanism based on the measurement by the speed measuring device under the centerless conditions that spindles are disengaged from the log.
Even when the actual rotating speed measured by the speed measuring device is deviated significantly from the theoretical rotating speed of the log specified by the peripheral drive system, the proposed apparatus adjusts the feed rate of the feed mechanism based on the measurement by the speed measuring device, that is, based on the actual rotating speed of the log. This structure effectively prevents errors in thickness of veneers peeled from the log.
Since substantially no errors in veneer sheet thickness are induced by the difference between the actual rotating speed and the theoretical rotating speed of the log, the proposed apparatus continues the veneer peeling operation until the log 11 has been peeled down to a minimum diameter. Another problem, however, arises in this apparatus.
While inducing no errors in veneer sheet thickness, a significant difference between the actual rotating speed and the theoretical rotating speed of the log lowers the productivity of veneers and makes the traces of engagement with the peripheral drive system obvious or conspicuous. In a flow system where a veneer lathe is coupled with a veneer cutter or another veneer processing apparatus for synchronous operations at a theoretical processing rate, the significant difference may cause an insufficient synchronism of the veneer lathe with the subsequent apparatus and thereby induce cracks and damages of the veneers.